RE: Blockbusting news, results get worse

Mudama, Eric
2003-10-29T20:11:32Z

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@ucw.cz]
>
> > > If you don't FLUSH CACHE, you have no guarantees your
> data is on the
> > > platter.
> >
> > I think that the idea that is floating around is to
> deliberately ruin
> > the formatting on part of the drive in order to simulate a
> bad block.
> >
> > Operation of disk drives immediately after a power failiure has been
> > discussed before, by the way:
> >
> > http://marc.theaimsgroup.com/?l=linux-kernel&m=100665153518652&w=2
>
> Well, that looks like pure speculation.
>
> BTW I *do* believe that powerfail can make the sector bad. Imagine you
> bump into bad sector during write, and need to reallocate...
>
> Pavel

Both the linked post and Pavel's point are correct.

In a modern drive, tolerances are so tight that your drive is constantly
re-writing blocks it knows it didn't write very well. In a power-fail
event, there's little to no time to reallocate or reattempt a write, and
even less energy available to "fix" things that aren't within specification
anymore (spin speed, etc) ... if we don't get the actuator to the latch,
your drive probably won't spin again and you'll lose *all* your data, so
that is our number 1 concern when the power fails.

"Performance" IDE drives these days ship with 8MB buffers, which compounds
the problem even further if you're trying to get data on the media after
power has been cut.